The move towards the use of new materials for chip manufacturing is necessary in order to solve the various issues generated by the continuous scaling up trend imposed on the industry. Accordingly, the expectation is that a number of different chemical elements will be introduced into the industrial semiconductor manufacturing process for many applications in the coming years. With regard to the next generation nodes, iridium is considered as one of the best candidates for the electrode capacitor for FeRAM and DRAM applications. Iridium has the required properties, such as high melting point, low resistivity, high oxidation resistance, and adequate work function, thereby making it a potential gate electrode material for CMOS transistor.
A large variety of iridium CVD precursors are available. Many of these have been studied for film deposition. Most of these iridium CVD precursors contain the ligand cyclopentadienyl (Cp). Recently, low melting point molecules were mentioned in Japanese patent JP 2001181841. Table 1 of JP 2001181841 discloses a table with the physical properties of iridium Cp type ligands.
VaporMelting pointpressureDecompositionMolecule(° C.)(Torr)(° C.)Ir(COD)(MeCp)400.08 at 100° C.XIr(COD)(EtCp)14 0.1 at 105° C.370Ir(1,3-CHD)(EtCp)150.1 at 75° C.300
Other types of cyclopentadienyl containing molecules are described in U.S. Pat. No. 6,329,286. The iridium precursors described in this patent are of the formula (MeCp)Ir(CO)2, which is described as a liquid at 58° C. Surprisingly, (MeCp)Ir(CO)2 is used dissolved in a solvent.
Bis(ethylene)(ethylcyclopentadienyl) iridium is described in U.S. Pat. No. 7,265,233. Bis(ethylene)(ethylcyclopentadienyl) iridium is an oil and its decomposition temperature, according to DSC measurements, is 220° C. When the ethyl group is replaced by a methyl group, the molecule is a solid.
U.S. Patent Application No. 2004/0215029 discloses precursors such as (EtCp)(1,3-cyclohexadiene) iridium, (MeCp)(1,3-cyclohexadiene) iridium, and (EtCp)(2,3-Me2-1,3-butadiene) iridium. (EtCp)(1,3-cyclohexadiene) iridium is described as an orange oil which decomposes from 300° C. (DSC), whereas (MeCp)(1,3-cyclohexadiene) iridium is a solid. (EtCp)(2,3-Me2-1,3-butadiene) iridium is an orange oil that decomposes from 310° C.
Other precursors are also available, such as β-diketonate type precursors among which are Ir(acac)3 and Ir(tmhd)3. (“New MOCVD precursor for Iridium thin film deposition”, X. Yan, Q. Zhang, X. Fan, Materials Letters 61 (2007), pp. 216-218). These precursors usually exhibit a very high melting point and are not adequate for metallic depositions.
Basing their research on the improvement of the β-diketonate type molecules, some researchers developed heteroleptic molecules of the type (keim)Ir(COD), (hfda)Ir(COD), and (amak)Ir(COD) (“Deposition of Iridium Thin Films Using New Irl CVD Precursor”, Y. Chi et al, CVD, 2002, 8(1), pp. 17-20). Such molecules have a lower melting point than homoleptic β-diketonate type molecules, 117° C., 111° C., and 127° C., respectively. Such a decrease in melting point, as well as the increase of volatility, is obtained thanks to the introduction of fluoromethyl instead of methyl.
Prior art precursors present a variety of different issues with regard to their integration into the semi-conductor industry. For example, precursors such as the β-diketonate type, have very high melting points; 270° C. for Ir(acac)3 and 235° C. for Ir(tmhd)3. For this reason, all of the delivery parts of the deposition tool upstream of the deposition chamber, as well as the delivery parts downstream, have to be heated to avoid absorption of the precursor onto the surface of the tube. As a result, the burden on the thermal budget becomes very important. In addition, these heated parts generate safety, as well as handling, issues. The deposition rate using these complexes is typically very low, thereby increasing a burden on the deposition process. Such precursors usually exhibit a very long incubation time.
On the other hand, some of the Cp type precursors allow for appreciable results compared to the β-diketonate type. Some of these precursors are liquid, which is an improvement with regard to the delivery of the precursor. However, the reactivity of the molecules on the substrate is still too low which results in bad nucleation of the iridium films on the substrates.
The precursors developed and set forth by Chi et al in Deposition of Iridium Thin Films Using New Irl CVD precursors, while representing an improvement of the β-diketonate type precursors, still present issues from the view point of their bad thermal stability and the incorporation of fluor elements that may be a source of impurity for the film or the sub-layers. Y. Chi et al, CVD, 2002 8 (1), pp. 17-20.
Accordingly, there is a need for a new type of iridium precursor which is stable and has a melting point below 25° C., preferably below 0° C.